The present invention relates to a method and apparatus for automatically dividing a machining process executed to obtain a predetermined product shape from a material shape of a workpiece. The method and apparatus are applied to an automatic programming apparatus.
In the prior art, numerical control (NC) machine tool having two main spindles facing each other have been proposed. In such a NC machine tool, while holding a workpiece with a chuck of one of the main spindles (hereinafter, referred to as a first main spindle), part of the workpiece not held by the chuck of the first main spindle is machined. The workpiece is then received by a chuck of the other main spindle (hereinafter, referred to as a second main spindle), and while the workpiece is held by the chuck of the second main spindle, part of the workpiece not held by the chuck of the second main spindle is machined. In this specification, the process for machining part of the workpiece not held by the chuck of the first main spindle will be referred to as a first process, and the process for machining part of the workpiece not held by the chuck of the second main spindle will be referred to as a second process.
Japanese Laid-Open Patent Publication No. 4-25346 discloses an interactive automatic programming apparatus that automatically divides the machining process for the workpiece into the first process and the second process.
This apparatus requires an operator to enter the profile line of the material shape of the workpiece and the profile line of the product shape to be obtained by machining. On the profile line of the product shape is defined a starting point (input starting point) for inputting the profile line. When the product shape has a through hole, for example, the input starting point is defined at an arbitrary portion on the inner profile line of the product shape that defines the through hole. Also, a portion on the outer profile of the product shape where the dimension of the outer profile is the greatest and that is furthest from the reference end face of the product shape in the axial direction of the workpiece is defined as the outer process division point. Furthermore, an inner division line that passes through the input starting point and is perpendicular to the axis of the workpiece is defined, and an outer division line that passes through the outer process division point and is perpendicular to the axis of the workpiece is defined. Part of the workpiece to be machined is divided into a fist area to be machined in the first process and a second area to be machined in the second process with the inner and outer division lines serving as boundaries.
Furthermore, International Publication No. 2002/095512 discloses a programming apparatus that creates a machining program for a multi-tasking machine that is capable of executing both milling and turning. In this apparatus, based on the material shape of the workpiece and the product shape to be obtained by machining, part of the workpiece to be machined is divided into a milling area and a turning area. In the apparatus of the above publication No. 4-25346, a portion on the outer profile of the product shape where the dimension of the outer profile is the greatest and that is furthest from the reference end face of the product shape in the axial direction of the workpiece is defined as the outer process division point. That is, in the apparatus of this publication, the outer process division point is defined without considering the volume of the machining target area in the first process and the volume of the machining target area in the second process. Therefore, a significant difference may be caused between the volume of the machining target area in the first process and the volume of the machining target area in the second process. This causes a significant difference between the machining time required for the first process and the machining time required for the second process, resulting in the decrease of the machining efficiency.
International Publication No. 2002/095512 simply discloses a method for dividing the machining target part of the workpiece into the milling area and the turning area, and does not disclose a method for dividing the machining process taking into consideration of the volume of the machining target parts.